1. Field of the Invention
The present invention relates to a data transmission apparatus, a data transmission method, and a program, and particularly relates to a data transmission technology relating to coded video contents.
2. Description of the Related Art
In the past, the method of forcibly changing a coding mode (coding method) to an intra-coding mode (intra-image coding mode) based on error information transmitted from the reception side for transmitting and/or receiving data relating to coded video contents has been proposed.
The above-described method has been used to decrease the number of frames through which an error propagates. The processing of the method is performed as below (refer to Japanese Patent Laid-Open No. 2003-23639, for example). When data that had not been appropriately received on the reception side (including data that is lost halfway through the transfer and that does not reach the reception side) is detected, an apparatus provided on the reception side transmits information determining the unreceived data (error information) to an apparatus provided on the transmission side (feedback). Upon receiving the error information transmitted from the apparatus provided on the reception side, the apparatus provided on the transmission side forcibly changes the coding mode of the next frame for coding to the intra-coding mode and performs data coding. Here, when the next frame for transmission had already been coded and the coding mode of the frame is not the intra-coding mode, the frame is decoded and the coding mode is changed to the intra-coding mode, and data recoding is performed.
Further, for transmitting and/or receiving data relating to coded video contents, the code amount is often controlled on the reception side, so as to reproduce the data at a desired frame rate. According to the above-described code amount control, frame rate information relating to a frame rate at which data is actually reproduced on the reception side is transmitted to the transmission side. Upon receiving the frame rate information, the amount of generated code is appropriately adjusted on the reception side based on the frame rate information.
However, in the above-described known method, the coding mode of the next frame for coding is forcibly changed to the intra-coding mode based on the error information when an error occurs. Although the error propagation can be stopped through the above-described method, the code amount is abruptly increased. In that case, the communication line is tightened, which may increase delayed transfers and data losses.
Further, when the communication path capacity (bandwidth) is limited and the coding mode is forcibly changed to the intra-coding mode, the code amount is abruptly increased. Therefore, the code amount that should be distributed to the frames from then on is decreased, which may significantly degrade the image quality. Further, the current bandwidth is estimated on the reception side based on the actual frame rate information. Therefore, when the transmission bit rate control is achieved by increasing and/or decreasing the frame rate, it has been difficult to delicately control the code amount in frames.